Ordinary Portland Cement – Manufacture, Properties, Types and Uses

Ordinary Portland cement is one of the most widely used type of Cement. In 1824 Joseph Aspdin gave the name as Portland cement as it has similarity in colour and quality found in Portland stone, which is a white grey limestone in island of Portland, Dorset. In this article we discuss about manufacture,constituents, properties, types , uses,advantages, disadvantages of Ordinary Portland cement.

Constituents and Properties of Ordinary Portland Cement

The constituents of ordinary portland cement are ,

Table 1 : Constituents of OPC cement

Constituents

Percentage

Calcium oxide, CaO

61–67%

Silicon dioxide, SiO2

19–23%

Aluminium oxide, Al2O3

2.5–6%

Ferric oxide, Fe2O3

0–6%

Sulfur (VI) oxide, SO3

1.5–4.5%

The properties of ordinary portland cement are,

Table 2 : Properties of OPC cement

Properties

Values

Specific Gravity

3.12

Normal Consistency

29%

Initial Setting time

65min

Final Setting time

275 min

Fineness

330 kg/m2

Soundness

2.5mm

Bulk Density

830-1650 kg/m3

Manufacture of OPC cement

Majorly there are 5 steps involved in the manufacture of OPC cement,

1.Crushing and grinding of raw material

In the first step of the manufacture of cement, the raw materials are crushed and grinded into small suitable size particles. There are 3 type of manufacture process of cement

Dry Process

Wet Process

Semi wet Process

Crushing and grinding process varies depending upon the type of manufacturing process. For dry process the raw materials are dried up before crushing.

Fig 1: Flow chart of Manufacture of OPC cement.

2. Mixing or Blending

In this step, the grinded raw material (lime stone) is blended or mixed with clay in the desired proportion ( limestone :75%, clay : 25%) and mixed well by the help of compressed air to get a homogeneous mix. In the dry process these mixes are stored in silos; slurry tanks are used in the wet process. The resulting material is known as slurry having 35-40% water.

3. Heating

This is the main important step in the manufacture of OPC cement, the product obtained from the mixing is passed into the Kiln by the help of conveyor belts.

Firstly the mix is preheated to 550C ,where all the moisture content is evaporated and clay is broken into silica, aluminium oxide, iron oxide.

In the next zone the temperature is rised to 1500 degree Celsius where the oxides form respective silicate, aluminates & ferrite.

In the final step the product is cooled down to 200C , where the end product obtained in the kiln is known as cement Clinkers, which is in the form of greenish black or grey colored balls.

4. Grinding

In this step the cement clinkers and Required amount of gypsum is mixed and grinded into very fine particles which are stored in the silos and later packed in cement bags and distributed.

The Expiry date of OPC cement is normally 3 months.

Types of Ordinary Portland Cement

The differentiation of OPC cement is based on the different codes of different countries.

1. AS per ASTM 150 (American Standards)

Type I Portland cement is known as common or general-purpose cement. It is generally assumed unless another type is specified.

Type II provides moderate sulfate resistance, and gives off less heat during hydration.

Type III has relatively high early strength. This cement is similar to type I, but ground finer.

Type IV Portland cement is generally known for its low heat of hydration.

Type V is used where sulfate resistance is important. This cement has a very low (C3A) composition which accounts for its high sulfate resistance.

2. As per EN 197 norm ( European norm)

CEM I Comprising Portland cement and up to 5% of minor additional constituents.

CEM II Portland cement and up to 35% of other single constituents

CEM III Portland cement and higher percentages of blastfurnace slag

CEM IV Portland cement and up to 55% of pozzolanic constituents

CEM V Portland cement, blastfurnace slag or fly ash and pozzolana

3. As per CSA A3000-08 ( Canadian standards)

GU, GUL > General use cement

MS > Moderate sulphate resistant cement

MH, MHL > Moderate heat cement

HE, HEL > High early strength cement

LH, LHL > Low heat cement

HS > High sulphate resistant; generally develops strength less rapidly than the other types.

Uses or Advantages

It is used for general construction purposes where special properties are not required such as reinforced concrete buildings, bridges, pavements, and where soil conditions are normal.

Used for most of concrete masonry units

It has great resistance to cracking and shrinkage but has less resistance to chemical attacks.

Initial setting time of OPC is faster than PPC so it is recommended in projects where props are to be removed early.

Curing period of OPC is less than PPC and curing cost reduces. Hence recommended where curing cost prohibitive.

Disadvantages

It cannot be used for mass concreting as it has high heat of hydration as compared to PPC.

The durability of concrete made using OPC is less than that of the concrete made using PPC.